Effect of Increased Dietary Protein on Tolerance to Intensified Training.

PURPOSE:: The purpose of the present study was to examine the impact of increased protein intake on short-term decrements in endurance performance during a block of high intensity training. METHODS:: Trained male cyclists (VO2max: 64.2+/-6.5 ml.kg.min) completed two, three-week trials, both divided equally into normal (NOR), intensified (INT) and recovery (REC) training. In a counter-balanced, crossover experimental design, cyclists received either a high protein (PRO) (3 g protein.kg body mass (BM).day) or a normal diet (CON) (1.5 g protein.kg BM.day) during INT and REC. Dietary carbohydrate content remained constant at 6 g.kg BM.day. Energy balance was maintained during each training week. Endurance performance was assessed with a VO2max test and a pre-loaded time trial. Alterations in blood metabolite responses to exercise were measured at rest, during and following exercise. Cyclists completed the Daily Analysis of Life Demands for Athletes (DALDA) questionnaire each day. RESULTS:: Increased dietary protein intake led to a possible attenuation (4.3%; 90% confidence limits x//5.4%) in the decrement in time trial performance following a block of high-intensity training compared with NOR (PRO=2639 +/- 350 s; CON=2555 +/- 313 s). Restoration of endurance performance during recovery training possibly benefited (2.0%; x//4.9%) from additional protein intake. Frequency of symptoms of stress described as 'worse than normal' reported following a block of high-intensity training was very likely (97%) attenuated (17; +/-11 AUC of 'a' scores part B, DALDA for INT+REC) by increasing the protein content of the diet. No discernable changes in blood metabolite concentrations were observed in PRO. CONCLUSION:: Additional protein intake reduced symptoms of psychological stress, and may result in a worthwhile amelioration of the performance decline experienced during a block of high-intensity training.